Method for producing cold and installation therefor

ABSTRACT

The method is implemented in an installation comprising an endothermic component (EC) and an exothermic component consisting of the reactors ( 1 ) and ( 2 ). The reactors ( 1 ) and ( 2 ) are in thermal contact, each of them constituting an active thermal mass for the other, and they are provided with heating means ( 6 ) and heat extraction means ( 5 ). ( 1 ), ( 2 ) and (EC) are provided with means for bringing them into selective communication, and reversible phenomena involving a gas G take place therein, the equilibrium curve for the phenomenon in ( 1 ) lying within a higher temperature range than that of the equilibrium curve for the phenomenon in ( 2 ), which is itself higher than that of the curve for the phenomenon in (EC) in the Clausius-Clapeyron plot.

The invention relates to an installation and a method of refrigerationusing a thermochemical system, especially for freezing various productsor for producing chilled water.

Heat generation or refrigeration installations based on a liquid/gasphase change or on reversible sorption between a gas, called the workinggas, and a liquid or solid sorbent, are known. A reversible sorption maybe an absorption of a gas by a liquid, an absorption of a gas on asolid, or a reaction between a gas and a solid. A reversible sorptionbetween a sorbent S and a gas G is exothermic in the synthesis directionS+G→SG and is endothermic in the decomposition direction SG→S+G. In aliquid/gas phase change of the gas G, the condensation is exothermic andthe evaporation is endothermic.

These reversible phenomena can be represented on a Clausius-Clapeyronplot by their equilibrium line:${{InP} = {f\left( {{- 1}/T} \right)}},{{{more}\quad{precisely}\quad{InP}} = {{- \frac{\Delta\quad H}{RT}} + \frac{\Delta\quad S}{R}}},$P and T being the pressure and the temperature respectively, ΔH and ΔSbeing the enthalpy and the entropy of the phenomenon (decomposition,synthesis, evaporation, condensation), respectively, and R being theperfect gas constant.

The endothermic step may be advantageously employed in an installationof this type for freezing various products (especially water forobtaining ice) or for producing chilled water.

Various reactors and methods based on these principles have beendisclosed.

EP 0 810 410 discloses a system comprising a reactor and anevaporator/condenser connected via a pipe provided with a valve. Athermochemical reaction or a solid/gas adsorption takes place in thereactor. The latter includes means for heating the solid that itcontains and means for extracting the heat from the exothermic synthesisreaction, these means being formed either by a heat exchanger, or byincreasing the thermal mass of the reactor. The reactor is designed insuch a way that, with its content, it has a thermal mass sufficient toabsorb the heat produced during the exothermic reaction. The method ofmanaging this system consists in bringing the evaporator/condenser intocommunication with the reactor when the evaporator/condenser is filledwith the working gas in liquid form, this having the effect of coolingthe evaporator/condenser by evaporation, and then in turning on themeans intended to heat the solid so as to deliver the working gas to theevaporator/condenser and to condense it therein. The means intended toheat the solid in the reactor are turned on before the previous step hasbeen completed. The refrigeration produced by the evaporator/condensercan be used to produce chilled water or ice. However, in this system,the cycle times are relatively long because the regeneration of thesystem takes place at a high temperature T_(h) and the cooling of thereactor takes place at ambient temperature T₀. Consequently, the reactorundergoes a relatively large thermal excursion between the regenerationtemperature and the ambient temperature. This results in a lowperformance coefficient.

EP-0 835 414 discloses a method of refrigeration and/or heat productionusing thermochemical phenomena involving a gas G in an installationcomprising two reactors (R₁, R₂) containing a respective salt (S₁, S₂),an evaporator for the gas G and a condenser for the gas G. Theequilibrium temperature of the salt S₁ is below the equilibriumtemperature of the salt S₂ at a given pressure. The reactors are placedin thermal contact so as to be able to exchange heat. The reactors, theevaporator and the condenser are brought selectively into communicationwith each other by means of pipes provided with valves. In the initialstate, the reactors and the condenser are in communication, at thepressure of the condenser. During operation, one of the reactors is insynthesis mode while the other reactor is in decomposition mode. In thisoperation mode, refrigeration is achieved at a single temperature level,that is to say at the evaporation temperature in the evaporator.

The object of the present invention is to provide a method and aninstallation for achieving a very high refrigeration power per unitvolume, for example around 200 kW/m³, with greatly reduced cycle timesand higher performance levels, especially for instantaneous and rapidproduction of chilled water or for the fast freezing of various products(for example for the production of ice).

According to the present invention, the method of refrigeration using athermochemical system comprises three reversible phenomena involving thegas G in three chambers (EC), (1) and (2), the respective equilibriumtemperatures T_(E(EC)), T_(E(1)) and T_(E(2)) at a given pressure beingsuch that T_(E(EC))<T_(E(2))<T_(E(1)), the chambers (1) and (2) being inthermal contact. The method is distinguished by the fact that, startingfrom a state in which the three chambers are at ambient temperature andat the same pressure:

-   -   in a first step, the chamber (1) is isolated and the chambers        (EC) and (2) are brought into communication in order to carry        out the exothermic synthesis in (2), the heat produced being        absorbed by the chamber (1);    -   in a second step, the chamber (2) is isolated and the chambers        (EC) and (1) are brought into communication in order to carry        out the exothermic synthesis in (1), the heat produced being        absorbed by the chamber (2); and    -   in a third step, the three chambers are brought into        communication and thermal energy is supplied to the chamber (1)        in order to carry out the exothermic decomposition steps in (1)        and in (2), for the purpose of regenerating the installation,        which is then left to return to the ambient temperature.        More precisely:    -   during a preliminary step, the three chambers are isolated from        one another and placed at the ambient temperature, said chambers        containing SEC+G, S1 and S2 respectively;    -   during a first step, the chambers (EC) and (2) are brought into        communication, the chamber (1) remaining isolated, in order to        carry out the exothermic synthesis in (2) and refrigeration in        the chamber (EC) at the equilibrium temperature in (EC)        corresponding to the pressure in the assembly formed by (2) and        (EC);    -   during a second step, the chamber (2) is isolated and the        chambers (EC) and (1) are brought into communication in order to        carry out the exothermic synthesis in (1) and refrigeration in        the chamber (EC) at the equilibrium temperature in (EC)        corresponding to the pressure in the assembly formed by (1) and        (EC);    -   during a third step, the three chambers are brought into        communication in order to carry out the synthesis in (EC) and        the decomposition in (2), and thermal energy is supplied to (1)        in order to carry out the decomposition in (1); and    -   during a fourth step, the three chambers are isolated and left        to cool down to the ambient temperature.

The refrigeration cycle is thus complete.

The reversible phenomenon in the reactors (1) and (2) may be areversible sorption chosen from reversible chemical reactions betweenthe gas G and a solid, the adsorptions of the gas G on a solid, andabsorptions of the gas G by a liquid.

The reversible phenomenon in the device (EC) may be a sorption, such asthat defined above, or a liquid/gas phase change of the gas G.Liquid/gas phase changes are preferred as they allow refrigeration at ahigher rate than with sorptions, because of the lower thermal inertia ofthe system.

In the rest of the text, “sorption” will denote a reversible sorption,the term “phenomenon” will denote a reversible phenomenon, chosen fromsorptions and liquid/gas phase changes, the term “L/G change” willdenote the liquid/gas phase change of the gas G, the terms “S1”, “S2”and “SEC” will denote the sorbent in the gas-lean state or, whereappropriate, G in the gaseous state, in the reactor (1), the reactor (2)and the device (EC) respectively, the terms “S1+G”, “S2+G” and “SEC+G”will denote the sorbent in the gas-rich state or, where appropriate, Gin the liquid state, in the reactor (1), the reactor (2) and the device(EC) respectively.

As an example of gas G, mention may be made of ammonia (NH₃) and itsderivatives, hydrogen (H₂), carbon dioxide (CO₂), water (H₂O), hydrogensulfide (H₂S), methane and other natural gases. As sorption reaction,mention may be made of reactions involving ammonium compounds (forexample chlorides, bromides, iodides or sulfates), hydrates, carbonatesor hydrides.

The method according to the present invention may be implemented usingan installation that comprises an endothermic component, consisting of adevice (EC), and an exothermic component, consisting of a reactor (1)and a reactor (2). Said installation is distinguished by the fact that:

-   -   the reactors (1) and (2) are in thermal contact so that each of        them constitutes an active thermal mass for the other;    -   the reactors (1) and (2) and the device (EC) are provided with        means for bringing them selectively into communication;    -   the reactor (1) and the reactor (2) are provided with heating        means (6) and heat extraction means (5); and    -   at the start of the cycle:        -   the reactors (1) and (2) contain a sorbent S1 and a sorbent            S2, respectively, capable of participating in a reversible            sorption involving a gas G, the equilibrium curve of the            reversible sorption in (1) lying within a higher temperature            range than that of the equilibrium curve of the reversible            sorption in (2) in the Clausius-Clapeyron plot; and        -   the device (EC) contains a compound G capable of undergoing            a liquid/gas phase change or an SEC+G sorbent rich in gas G            capable of participating in a reversible sorption, the            equilibrium temperature of which is below the equilibrium            temperature of the reversible sorption in the reactor (2).

In one particular embodiment, the thermal contact between the reactors(1) and (2) is achieved by placing the reactor (1) inside the reactor(2). For example, the reactors (1) and (2) may be concentric, thereactor (1) being placed inside the reactor (2).

In another embodiment, each of the reactors (1) and (2) is formed byseveral hollow plates containing the respective sorbents, plates of oneof the reactors alternating with the plates of the other. The thicknessof the plates is typically about 1 to 3 cm.

In an installation according to the invention, refrigeration takes placein the device (EC). If the refrigeration is intended for producing iceor chilled water, the installation furthermore includes a reservoir (3)containing water in direct thermal contact with the device (EC). If itis desired to produce ice, it is preferred to use a reservoir (3)divided into compartments having the size of the desired pieces of ice.When the installation is used to manufacture chilled water, thereservoir R may be a coil, incorporated into the wall of the device(EC), water flowing through said coil. If the installation is intendedto freeze various products, the reservoir (3) has a suitable shape forcontaining and freezing the products correctly.

FIG. 1 shows a diagram of an installation according to the invention.

In this figure, the installation comprises a reactor (1), provided withheating means (6), a reactor (2), in thermal contact with the reactor(1) and provided with cooling means (5), a device (EC) and pipesprovided with valves V1 and V2 for bringing the reactors (1) and (2)selectively into contact with (EC). The reactor (1) contains a sorbentS1 capable of undergoing sorption with a gas G. The reactor (2) containsa sorbent S2 capable of undergoing sorption with the gas G, theequilibrium temperature of S1 being above the equilibrium temperature ofS2 at a given pressure. The device (EC) contains the gas G in the liquidstate or a sorbent SEC capable of undergoing sorption with the gas G,the equilibrium temperature of SEC being below the equilibriumtemperature of S2 and a given pressure. The device (EC) isadvantageously an evaporator/condenser (noted hereinafter by evaporator)in which a liquid/gas (L/G) phase change takes place. (EC) is in directthermal contact with a reservoir (3) incorporated into its wall andcontaining water.

The installation and the method according to the invention areparticularly advantageous when the device (2) is an evaporator/condenser(denoted hereinafter by evaporator). In one particular embodiment, theevaporator has a structure as shown in FIGS. 2 and 3. FIG. 2 shows across-sectional view and FIG. 3 shows a longitudinal sectional view.

The evaporator consists of a cylinder (8) which is closed at its twoends and has a circular cross section. The circular cross sectionincludes, in its upper part, a concave circular arc corresponding to thecross section of the ice tray (7). Hollow fins (9) are placed inside theevaporator, in the longitudinal direction. A tube (10) connected to thepipe for transferring the gas G between the evaporator and the reactors(1) or (2) runs into the cylindrical chamber of the evaporator via abore made in one of the ends of the cylinder, and it is placed directlybeneath the wall of the ice tray (7). The working gas G, in the form ofa boiling liquid, is placed in the bottom of the evaporator. The spacebetween the walls of the fins is occupied by the phase change materialM.

The outer wall of the evaporator (8) is made of a material having a highthermal diffusivity, that is to say a low thermal capacity in order toallow the wall temperature to drop rapidly and a high thermalconductivity in order to allow rapid ice formation. A material, forexample based on aluminum, which has a low thermal capacity and a highconductivity, is suitable because of its compatibility with ammonia,which is a gas frequently used in negative-temperature refrigerationinstallations. The fins (9) increase the diffusion of heat, from theboiling liquid into the ice tray, and the mechanical strength of theevaporator.

The ice tray 7 is provided with many transverse partitions placed so asto obtain the desired shape of the pieces of ice. The overall shape ofthe ice tray has a suitable toroidal half-moon shape, thereby allowingeasy demolding of the pieces of ice formed.

The phase change material M placed between the walls of the hollow finsmaintains the temperature of the evaporator at a low temperature. Thismakes it possible to extend the ice production step during the transientheating step for regenerating the reactor isolated from the evaporator.

The particular configuration of the tube (10) and its position in thechamber of the evaporator are such that the hot gases, coming from thereactor during the step 5 of bringing the high-pressure reactor intocommunication with the evaporator maintained at low pressure by thephase change material, firstly strike the wall of the ice tray, whichmakes it easier to separate the pieces of ice.

In one particular embodiment, the method of refrigeration according tothe invention is implemented using an installation as described above,in which the chamber (EC) furthermore contains a solid/liquid phasechange material M. The phase change material M is chosen in such a waythat the solidification temperature is at least slightly below thetemperature of refrigeration in (EC) corresponding to the synthesis in(2). A temperature difference of a few degrees, for example from 1° C.to 10° C., is appropriate. For example, this temperature is 0° C. whenthe desired objective is to manufacture ice. Material M may be chosen,for example, from paraffins, such as n-alkanes having from 10 to 20carbon atoms, eutectic mixtures and eutectic solutions. The processtakes place in the same manner as in the general case described above.However, during the regeneration step, the temperature in the chamber(EC) is that of the melting point of the material M, resulting in aregeneration temperature which is less than that occurring in theabsence of the change of phase material. This alternative way ofimplementing the method of the invention consequently reduces the cycletime and the amount of energy required for regeneration.

The implementation of the method of the invention in an installationaccording to the invention is described in greater detail below withreference to FIGS. 4 to 7 in the case of an installation in which (EC)is an evaporator/condenser. FIGS. 4 to 7 show the position of theinstallation in the Clausius-Clapeyron plot during the various steps ofan operating cycle. The curves in the plots correspond to monovariantphenomena. The operation of the installation would, however, beidentical if a divariant phenomenon, corresponding for example to theabsorption of the gas G by an absorbent solution (for example water/NH₃or water/LiBr) or to the adsorption of the gas G on the surface of anactive solid (for example active carbon or zeolite), were to be used inthe reactors (1) and/or (2).

Initial Step:

During an initial step, the components (1), (2) and (EC) are placed atthe ambient temperature T₀ and isolated from one another by keeping thevalves V1 and V2 closed. Since the components are isolated from oneanother, they are at their respective equilibrium pressures at T₀,denoted by PE⁰, P1 ⁰ and P2 ⁰. The reactors (1) and (2) contain S1 andS2 respectively while the device (EC) contains G in liquid form. S1, S2and G are chosen in such a way that P1 ⁰<P2 ⁰<PE⁰. The situation of thecomponents is shown by 1 ⁰, 2 ⁰ and E⁰ in the plot shown in FIG. 4.

Step 1: First Refrigeration Step

The valve V1 remains closed and the installation operates by means ofthe reactor (2) and the evaporator (EC). Opening the valve V2 equalizesthe pressure (PE¹=P2 ¹) between (EC) and (2). The evaporator (EC) passesfrom the position E⁰ to E¹ and the reactor (2) from the position 2 ⁰ to2 ¹. The change in the respective positions is shown in FIG. 4. In the 2¹ state, the reactor (2) is in synthesis position, whereas in the E¹state the evaporator (EC) is in the evaporation state. Bringing (EC)into communication with (2) causes a sudden drop of temperature in (EC)and the temperature passes from T₀ to T_(E1). This temperature drop thusfirstly allows rapid freezing of the water contained in a tray (notshown in FIG. 1) incorporated into the wall of the evaporator. A firstrefrigeration power peak is then observed. The gas liberated by theevaporation in (EC) is absorbed by the sorbent S2 contained in (2),causing a temperature rise in the reactor (2) owing to the fact that thesorption is highly exothermic. The energy produced by the sorption in(2) is absorbed by the reactor (1), which is isolated from (EC) but inthermal contact with (2). The reactor (1) therefore constitutes athermal capacitance allowing the reactor (2) to remain far apart fromits thermodynamic equilibrium. The reactor (1) then passes from theposition 1 ⁰ to the position 1 ¹ by remaining on its thermodynamicequilibrium line.

Step 2: Second Refrigeration Step

When synthesis has been completed in the reactor (2) at the end of step1 [the duration of which is determined by the nature and the quantitiesof the elements used in (2) and (EC)], the valve V2 is closed and thevalve V1 immediately opened. The installation then operates by means ofthe reactor (1) and the evaporator (EC).

The equilibrium pressure that is established between the reactor (1) andthe evaporator (EC) makes these components pass from the positions shownby E¹ and 1 ¹ to the positions shown by E² and 1 ². This change is shownin FIG. 5.

Refrigeration takes place in the evaporator (EC) at E², that is to sayat a temperature T_(E2) below the refrigeration temperature T_(E1) instep 1. Since steps 1 and 2 take place one after the other, they givehigh levels of refrigeration power at T_(E2), driving (EC) only fromT_(E) ¹ to T_(E) ². During this step, the reactor (2) acts as a thermalcapacitance for the reactor (1). The reactor (2), which absorbs theexothermic reaction heat coming from the reactor (1), rises intemperature and is at 2 ² on its thermodynamic equilibrium line. Thanksto this thermal capacitance, the reactor (1) remains at 1 ², which is aposition far from its thermodynamic equilibrium. This results in astrong, second refrigeration power peak.

Step 3: Ice-Separation and Regeneration Step

At or before the end of step 2, valve V2 is opened, the valve V1remaining open.

The components (1), (2) and (EC) move rapidly to positions 1 ³, 2 ³ andC³ at an intermediate pressure level between that of step 1 and step 2.The contents of the reactor (2) are in the decomposition position andthe contents of the reactor (1) remain in the synthesis position. Thesesynthesis/decomposition positions remain far from equilibrium because ofthe thermal contact that exists between the reactors (1) and (2). Theresult is that the decomposition in the reactor (2) is more rapid thanthe synthesis that emanates in the reactor (1). Thus, condensation isimmediately initiated in the device (EC), which moves rapidly to theposition C³. This exothermic condensation is possible as the heat isabsorbed by the surface melting of the pieces of ice, causing them toseparate and thus making it easier to subsequently remove them from thedevice (EC). Turning the heating means (6) on in (1) right from thestart of this step (at the same time as the valve V2 is opened) resultsin condensation in (EC), which progressively moves from the position C³to a pressure level C⁴ that again allows the gas G to condense.Condensation is again possible when the reactor (1) is in the position 1⁴ and when the condensation pressure becomes greater than the saturationvapor pressure corresponding to the mean temperature of the coolingfluid of the element (EC) (for example that of the external air). Thetemperature T₁ ⁴ is the regeneration temperature (T_(reg)) and thedevice (EC) is in the position C⁴, which moves the reactor (2) to theposition 2 ⁴ also at the pressure level imposed by the condensation. Thethermodynamic position C⁴ is then necessarily such that the temperaturecorresponding to the position C⁴ is above the ambient temperature T₀,because the heat of condensation is transferred to the heat sink. Theregeneration of the device means that the heat of this exothermiccondensation must be extracted from a heat sink, which may be theambient air or a cooling circuit. The change in the position of thevarious components is shown in FIG. 6.

Step 4: Cooling Step and Return to the Initial Step

Once the regeneration of the reactors (1) and (2) has been completed,the valves V1 and V2 are closed. The reactors thus isolated are thencooled, either naturally or using cooling means (5) (fan, coolingcircuit, etc.), lowering the temperature and the pressure. Eachcomponent moves along its thermodynamic equilibrium curve until itreaches the ambient temperature and thus returns to the initialposition, E⁰, 1 ⁰ and 2 ⁰ respectively. The device is thus under theinitial conditions of the refrigeration storage step at the start of theoperating cycle. The change in position of the various components duringthis step is shown in FIG. 7.

When the method of the invention is employed with an installation inwhich the chamber (EC) furthermore includes a phase change material M,the phase change temperature T_(M) of which is at least slightly belowthe refrigeration temperature T_(E1) in (EC) corresponding to synthesisin (2), the regeneration of the sorbents contained in the reactors (1)and (2) is more rapid.

The successive states in which the reactors (1) and (2) and the chamber(EC) are found during the successive steps are illustrated in theClausius-Clapeyron plot shown in FIG. 8. In this embodiment, the device(EC) may have the configuration shown in FIGS. 2 and 3.

Initial Step:

This is similar to the initial step described above. The components (1),(2) and (EC) are in the positions shown by 1 ⁰, 2 ⁰ and E⁰ in FIG. 8.

Step 1: First Refrigeration Step

The valve V1 remains closed. The installation operates by means of thereactor (2) and the evaporator (EC).

Opening the valve V2 equalizes the pressure (PE¹=P2 ¹) between (EC) and(2). The evaporator (EC) passes from the position E⁰ to E¹ and thereactor (2) passes from the position 2 ⁰ to 2 ¹. In the 2 ¹ state, thereactor (2) is in the synthesis position, while in the E¹ state theevaporator (EC) is in the evaporation state.

Bringing (EC) into communication with (2) causes a sudden drop in thetemperature (EC), which passes from T₀ to T_(E1). This temperature dropthus firstly results in rapid cooling and then partial freezing of thewater contained in the tray 7 incorporated into the wall of theevaporator, then solidification of the material M. The gas released bythe evaporation in (EC) is absorbed by the sorbent S2 contained in (2),which results in a temperature rise in the reactor (2) because thesorption is highly exothermic. The energy produced by the sorption in(2) is absorbed by the reactor (1), which is isolated from (EC) but inthermal contact with (2). The reactor (1) therefore constitutes athermal capacitance allowing the reactor (2) to remain far from itsthermodynamic equilibrium. The reactor (1) then passes from the position1 ⁰ to the position 1 ¹, remaining on its thermodynamic equilibriumline.

Step 2: Second Refrigeration Step

The presence of a phase change material in (EC) does not modify theexecution of step 2. After this step, the reactors (1) and (2) and thechamber (EC) are in the respective positions 1 ², 2 ², E².

Step 3: Ice Separation and Regeneration Step

After step 2, the valve V2 is opened, the valve V1 remaining open.

The components (1), (2) and (EC) move rapidly to the positions 1 ³, 2 ³and C³ at an intermediate pressure level between that of step 1 and step2. The contents of the reactor (2) are in the decomposition position andthe contents of the reactor (1) remain in the synthesis position. Thesesynthesis/decomposition positions remain far from equilibrium, becauseof the thermal contact that exists between the reactors (1) and (2). Asa result, the decomposition in the reactor (2) is more rapid than thesynthesis that is completed in the reactor (1). Thus, condensation isimmediately initiated in the device (EC), which moves rapidly to theposition C³. This exothermic condensation is possible since the heat isabsorbed by the surface melting of the pieces of ice, causing them toseparate and thus making it easier for them to be subsequently removedfrom the device (EC). Turning the heating means (6) on in (1) right fromthe start of this step (at the same time as opening the valve V2)maintains the condensation in (EC), which continues to moveprogressively from the position C³ to the position C^(4′), againallowing gas to condense effectively.

Condensation is again possible when the reactor (1) is in the position 1^(4′) and when the condensation pressure becomes greater than thesaturation vapor pressure corresponding to the melting point T_(M) ofthe phase change material. The temperature T₁ ^(4′) is the regenerationtemperature (T_(reg)) and the device (EC) is in the position C^(4′),which takes the reactor (2) to the position 2 ^(4′), again at thispressure level imposed by condensation of the gas G.

Opening valve V2 (the valve V1 remaining open) and turning on theheating means (6) in the reactor (1) triggers rapid desorption in thereactor (2), separation and removal of the ice, and the end of thesynthesis in the reactor (1) followed by desorption in (1). Thecondensation temperature imposed at the temperature T_(M) by the meltingof the eutectic makes it possible, on the one hand, to condense the gasG at a temperature below the ambient temperature. This allows thethermal excursion of the device (EC) to be substantially reduced,resulting in better efficiency of the method and shorter cycle times. Onthe other hand, the condensation pressure P_(C4′) is lower than thepressure P_(C4) obtained in the case without a phase change material.This results in a decrease in the regeneration temperature of (1), andconsequently that of (2), which means a reduction in the energy consumedin regenerating (1) and (2), again resulting in a better efficiency ofthe method and a reduction in the cycle times.

Step 4: Cooling Step and Return to the Initial Step

The entire installation returns to the temperature T₀ in a shorter timeif a phase change material is present, because the reactor (1) is at alower temperature.

The installation according to the invention in its most generalconfiguration, operated according to the method of the invention, thusmakes it possible to achieve powerful refrigeration in very short times,which can allow the almost instantaneous production of ice for example.Furthermore, when the installation contains a phase change material inthe endothermic component, the regeneration temperature in the reactoroperating at the highest temperature is reduced, which on the one handshortens the duration of the process and reduces the power consumption.

1. A method of refrigeration using a thermochemical system comprisesthree reversible phenomena involving the gas G in three chambers (EC),(1) and (2), the respective equilibrium temperatures T_(E(EC)), T_(E(1))and T_(E(2)) at a given pressure being such thatT_(E(EC))<T_(E(2))<T_(E(1)), the chambers (1) and (2) being in thermalcontact, wherein, starting from a state in which the three chambers areat ambient temperature and at the same pressure: in a first step, thechamber (1) is isolated and the chambers (EC) and (2) are brought intocommunication in order to carry out the exothermic synthesis in (2), theheat produced being absorbed by the chamber (1); in a second step, thechamber (2) is isolated and the chambers (EC) and (1) are brought intocommunication in order to carry out the exothermic synthesis in (1), theheat produced being absorbed by the chamber (2); and in a third step,the three chambers are brought into communication and thermal energy issupplied to the chamber (1) in order to carry out the exothermicdecomposition steps in (1) and in (2), for the purpose of regeneratingthe installation, which is then left to return to the ambienttemperature.
 2. The method as claimed in claim 1, wherein: in theinitial state, the chambers (EC), (1) and (2) are isolated from oneanother and placed at the ambient temperature, the chambers (1) and (2)contain their respective sorbent S1 and S2 in the state lean in gas G,and the chamber (EC) contains G in the liquid state or the sorbent inthe state rich in gas G; during the first step, bringing the chambers(EC) and (2) into communication causes refrigeration in the chamber (EC)at the equilibrium temperature in (EC) corresponding to the pressure inthe assembly formed by (2) and (EC); during the second step, bringingthe chambers (EC) and (1) into communication causes refrigeration in thechamber (EC) at the equilibrium temperature in (EC) corresponding to thepressure in the assembly formed by (1) and (EC); and during the thirdstep, bringing the three chambers into communication causes synthesis in(EC) and decomposition in (2), and then applying thermal energy to (1)causes decomposition in (1).
 3. The method as claimed in claim 1,wherein the reversible phenomenon in the reactors (1) and (2) is chosenfrom reversible chemical reactions between the gas G and a solid,adsorptions of the gas G on a solid, and absorptions of the gas G by aliquid.
 4. The method as claimed in claim 1, wherein the reversiblephenomenon in the device (EC) is a liquid/gas phase change.
 5. Themethod as claimed in claim 1, wherein the reversible phenomenon in thedevice (EC) is a sorption chosen from reversible chemical reactionsbetween the gas G and a solid, adsorptions of the gas G on a solid, andabsorptions of the gas G by a liquid.
 6. An installation forimplementing the method as claimed in claim 1, comprising an endothermiccomponent comprised of a device (EC) and an exothermic componentconsisting of a reactor (1) and a reactor (2), wherein: the reactors (1)and (2) are in thermal contact so that each of them constitutes anactive thermal mass for the other; the reactors (1) and (2) and thedevice (EC) are provided with means for bringing them selectively intocommunication; the reactor (1) and the reactor (2) are provided withheating means and heat extraction means; and at the start of a cycle:the reactors (1) and (2) contain a sorbent S1 and a sorbent S2,respectively, capable of participating in a reversible sorptioninvolving a gas G, the equilibrium temperature of the reversiblesorption in (1) being higher than the equilibrium temperature of thereversible sorption in (2) at a given pressure; and the device (EC)contains a compound G capable of undergoing a liquid/gas phase change oran SEC+G sorbent rich in gas G capable of participating in a reversiblesorption, the equilibrium temperature of which is below the equilibriumtemperature of the reversible sorption in the reactor (2).
 7. Theinstallation as claimed in claim 6, wherein the device (EC) is in directthermal contact with a reservoir containing water.
 8. The installationas claimed in claim 6, wherein the device (EC) furthermore contains aliquid/solid phase change material, the phase change temperature ofwhich is below the refrigeration temperature.
 9. The installation asclaimed in claim 6, wherein the device (EC) is an evaporator which iscomprised of a cylinder which is closed at its two ends, the circularcross section of which cylinder includes, in its upper part, a concavecircular arc corresponding to the cross section of the ice tray, whichevaporator furthermore includes: the hollow fins being occupied by asolid/liquid phase change material; a tube, connected to a pipetransferring the gas G between the evaporator and the reactor (2), runsinto the cylindrical chamber of the evaporator via a bore made in one ofthe ends of the cylinder, which tube is placed directly beneath the wallof the ice tray, the working gas G in the form of a boiling liquid beingplaced in the bottom of the evaporator.
 10. The installation as claimedin claim 6, wherein the reactor (1) is placed inside the reactor (2).11. The installation as claimed in claim 10, wherein the reactors (1)and (2) are concentric, the reactor (1) being placed inside the reactor(2).
 12. The installation as claimed in claim 6, wherein each of thereactors (1) and (2) is formed by several hollow plates containing therespective sorbents, the plates of one reactor alternating with theplates of the other.
 13. The installation as claimed in claim 8, whereinthe difference between the phase change temperature of the phase changematerial and the refrigeration temperature is from 1° C. to 10° C.